An efficient and accurate semi-analytical matching technique for waveguide-fed antennas

Utilization of graphene covered waveguide inserts to form tunable waveguide resonators is theoretically explained and rigorously investigated by means of full-wave numerical electromagnetic simulations. Instead of using graphene-based switching elements, the concept we propose incorporates graphene sheets as parts of a resonator. Electrostatic tuning of the graphene surface conductivity leads to changes in the electromagnetic field boundary conditions at the resonator edges and surfaces, thus producing an effect similar to varying the electrical length of a resonator. The presented outline of the theoretical background serves to give phenomenological insight into the resonator behavior, but it can also be used to develop customized software tools for design and optimization of graphene-based resonators and filters. Due to the linear dependence of the imaginary part of the graphene surface impedance on frequency, the proposed concept was expected to become effective for frequencies above 100 GHz, which is confirmed by the numerical simulations. A frequency range from 100 GHz up to 1100 GHz, where the rectangular waveguides are used, is considered. Simple, all-graphene-based resonators are analyzed first, to assess the achievable tunability and to check the performance throughout the considered frequency range. Graphene–metal combined waveguide resonators are proposed in order to preserve the excellent quality factors typical for the type of waveguide discontinuities used. Dependence of resonator properties on key design parameters is studied in detail. Dependence of resonator properties throughout the frequency range of interest is studied using eight different waveguide sections appropriate for different frequency intervals. Proposed resonators are aimed at applications in the submillimeter-wave spectral region, serving as the compact tunable components for the design of bandpass filters and other devices.

A rectangular pyramidal horn antenna fabricated with tapered dielectric E-plane boundary walls whose inner surface is periodically loaded with thin conducting strips is investigated. For better impedance matching, at the throat region of the horn antenna, 3 cm portion is metallised. The radiation characteristics of this horn antenna are compared with that of an identical conventional horn antenna with conducting E-plane boundary walls. Considerable improvement in the E-plane radiation characteristics is observed. As H-plane boundary walls are not modified, no change in the H-plane radiation characteristics is observed. However,the conventional horn antenna shows slightly better impedance matching than the test horn antenna.

A relatively simple and efficient high‐frequency analysis of electromagnetic modal reflection and transmission coefficients for waveguide discontinuities which are formed by joining different waveguide sections is presented. The analysis extends the concept of geometrical theory of diffraction based equivalent edge currents and utilizes it in conjunction with the reciprocity theorem to describe interior (waveguide) scattering effects. It is noted that the previous use of equivalent edge currents was mostly restricted to exterior scattering by edged bodies, and its application to deal with interior scattering was limited to those guide geometries for which image theory could be used effectively to account for the interior wall effects. The present extension allows one to treat more general two‐ and three‐dimensional waveguide geometries provided the waveguide modes and their associated modal rays can be found explicitly. In particular, expressions for two‐dimensional reflection and transmission coefficients are developed, and numerical results are shown for a flanged, semi‐infinite parallel plate waveguide and for the junction between two linearly tapered waveguides. One sample result is also shown for the reflection coefficient of a three‐dimensional open‐ended circular waveguide. Detailed expressions for three‐dimensional waveguide discontinuities are being reported separately.

A rigorous approach combining the orthogonal expansion method for modeling cylindrical posts in rectangular waveguides and the extension of the three short plane technique is introduced to obtain the S-matrix for a general coaxial probe in a rectangular waveguide. A cascading procedure is applied to solve the problem of a probe near a waveguide discontinuity and to obtain the response of a probe-excited band pass filter. The computed results are in excellent agreement with the measured results showing the usefulness of this method.

The behavior of several lower order modes in a sectoral waveguide is investigated. It is shown that their sequence order depends on the flare angle of the sector. It is found that, at an angle smaller than 135°, the waveguide may operate in a single-mode regime with the H 01 mode. The per-unit-length attenuation of the H 01 mode in a sectoral waveguide is analyzed and compared to the attenuation of the H 10 mode in a rectangular waveguide.

An accurate design technique of dual-mode microwave dielectric or air-filled rectangular waveguide filters is described. Dual-mode coupling is realized by a section of rectangular waveguide with square-corner-cut. The unequal couplings between dual-mode pairs of the cavities is provided by a section of evanescent mode waveguide. Rigorous analyses are applied to characterize the microwave junctions and to obtain the design parameters for the filter. The design procedure used to determine the dimensions of the waveguide junctions with a minimum of computational effort is described. The design is demonstrated by four-pole and six-pole dual-mode rectangular waveguide elliptic function filters. Excellent agreement between computer simulation and experimental results with absolutely no tuning justifies the design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The computer‐aided analysis and design of direct‐coupled and quarter‐wave‐coupled bandpass filters utilizing monomode rectangular waveguides with 1‐dimensional offset discontinuities are described. The equivalent networks of these discontinuities, which consist of a shunt reactance and additional transmission lines connected at both sides, have been derived from the rigorous field‐theoretical investigations of E‐plane and H‐plane displacements in rectangular waveguide. Both network elements are tabulated in terms of geometry and wavelength with fine steps to allow accurate interpolation by means of computational methods, Simple design formulae for the filter geometry as a function of the electrical specifications are given which are based upon narrow‐band approximations. The analytical relationships required for a computer simulation of the filter's wide‐band performance are summarized. The predicted frequency characteristics showed such close agreement with the experimental results obtained on two X‐band filter models that neither tuning elements in the waveguide sections nor final adjustments of the offset widths had to be provided.

This letter is intended to point out a few typing mistakes in the above paper [1], which discusses computing the complex permittivity of a dielectric material embedded in a rectangular waveguide or a microstrip line, and to suggest corrections to its formulation.

A triband antenna with high gain and low profile is proposed. This antenna is based on the concept of Fabry–Perot cavity antenna (FPCA) and three resonances are obtained by employing two frequency selective surface (FSS) layers. Two FSS layers lead to two resonant frequencies by making each FSS layer satisfy the resonant condition of Fabry–Perot cavity. The third resonant frequency is obtained by exploiting the combined effects of the two FSS layers together. The operating principle of this proposed antenna is explained and the achievable frequency range is investigated. It is shown that the proposed method enables all three resonant frequencies to be independently tuned within certain frequency range. Because of the 0° reflection phase of the combined-FSSs, the present antenna has a low profile. To verify the design concept, one C-/X-/Ku-band FPCA is designed, fabricated and tested. Experimental results agree well with the simulated results. High gain with good impedance matching in three bands is obtained, which reaches a peak gain of 13.4 dBi at 5.2 GHz, 18.9 dBi at 9.7 GHz, and 20 dBi at 14.6 GHz. The overall height of the proposed antenna is approximately 0.36 wavelength at its lowest operating frequency.

The scattering properties of the H‐plane waveguide discontinuities such as the cross junction, T‐junction, and right‐angle bend are analyzed taking their symmetry into account. the solutions are synthesized in two new and simple expressions. These solutions are treated rigorously by the mode‐matching method in which each junction section is divided by a circular region and the electro magnetic fields are matched with the scattered waves into waveguide regions at the boundaries. By means of the accurate numerical results obtained in a wide frequency range, the scattering properties of the H‐plane junctions in a standard waveguide and an oversized waveguide are examined in detail. the latter is believed to be useful for an approximnte estimation of the scattering properties of crossing roads in underground shopping centers.

This paper investigates a novel waveguide component design with dual functionality of mode conversion and power splitting. Because of its complex internal geometry which conventional fabrication methods cannot realize, additive manufacturing was explored, specifically selective laser melting. The end-to-end process of design, simulation, fabrication, and measurement will be discussed in detail. The said waveguide component converts between 4 rectangular waveguide TE10 mode and 1 circular waveguide TM01 mode. The 1 to 4 splitter was done while achieving low power splitting losses and mode conversion losses with low return losses. This allows for waveguide connections to be made between circular waveguides and rectangular waveguides at X-Band, which can be used for radars or satellite communication applications. The novelty of this component design comes from impedance matching between 4 rectangular waveguides operating in the fundamental mode and 1 single highly over-moded circular waveguide by means of coaxial rod and matching fins. All these are done while keeping the overall size small, compact, and lightweight.

Recently, indoor wireless local area network (WLAN) and broadband communication systems operating at millimeter-wave frequencies have attracted much interests because they offer the advantage of high data rates. Two distinct technologies employing non radiative dielectric (NRD) guides and rectangular waveguides have been rigorously developed to efficiently achieve stringent radio-frequency (RF) system specifications [1,2]. Yoneyama et al. reported high-performance, low-loss millimeter-wave building blocks such as filters, voltage-controlled oscillators, mixers, modulators and antennas; these components can be integrated by the NRD technology. On the other hand, a single-substrate transceiver module for 76–77 GHz autonomous cruise control (ACC) radar applications was reported, where (monolithic microwave integrated circuits) MMICs and discrete devices were mounted in a multi chip module (MCM) fashion by wire-bonding and flipchip techniques. Both millimeter-wave module integration technologies are aimed for low-cost, high-volume and high-yield designs. The guiding technologies mentioned above perform well at millimeter-wave frequencies, however, some modules would require complicated analyses and mechanical fabrication processes, hence increasing the cost and complexity of the system integration efforts. For example, the well-known horn antennas are three-dimensional; thereby they need transitions to handle mode conversion and impedance matching from waveguides to planar circuits and vice versa [3]

This article presents a theoretical and experimental comparative study of the different multipactor threshold values obtained in the rectangular waveguide (RW) and the groove gap waveguide (GGW). To this end, the multipactor effect has been first analyzed in an RW with a recently developed theoretical model. Then, the multipactor breakdown power levels in the equivalent GGW have been predicted with an accurate electron tracking code, showing a significant increment compared with the RW case. In order to validate these results, two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -plane WR-90 RW transformers have been designed with a full-wave electromagnetic simulation tool. The central sections of these transformers have been implemented in RW and GGW, respectively, and their multipactor breakdown power levels have also been predicted. The two designed transformers have been fabricated in aluminum and then measured in terms of electrical response (scattering parameters) and RF multipactor effect (power threshold values). All the experimental results agree well with the set of simulated data, thus fully validating the performed study.

A new polarization filter with no element inside the circular waveguide is presented. It is realized by the insertion of rectangular waveguide sections in a circular waveguide. The validity of this new design is verified on a prototype model.

Latching phase shifters, consisting of a waveguide section containing a ferrite toroid, are widely used as digital steering elements in microwave array antennas. The theoretical determination of device performance cannot be obtained exactly, since these structures are inhomogeneous along both transverse directions. The present study presents an approximate method to evaluate phase shift and losses in the case of a rectangular toroid. An approximately equivalent structure (twin slab), for which an exact resolution method is available, is considered first. The changes due to the upper and lower sections of the toroid are then evaluated by means of a variational principle. Experimental results show good agreement with computed values for several practical cases considered. Finally, the range of validity for this approximate method is determined.